FAQs • Cowlitz County, WA • CivicEngage

Can I build an Accessory Dwelling Unit (ADU) on my property?

Probably! Accessory dwelling units can be either attached to a primary residence or detached as a separate structure. Classic examples are a dwelling above a garage, or a cottage for rental income. ADU’s require planning approval and a residential building permit. They can be manufactured or modular homes.
The maximum size of an ADU is 1,200 square feet.
In areas classified as Urban and Suburban in the Comprehensive Plan, you may choose to build up to two ADU’s – one attached and one detached. In all other areas of the county, one ADU is allowed.
There is no restriction on owner-occupancy of the primary residence or the ADU – one or both can be occupied by tenants.
If you are using a domestic well and/or onsite septic system for the ADU, you will need to talk with the Environmental Health Unit about their requirements. Their email is omseptic@cowlitzwa.gov and phone number is 360-414-5599 - press 5 and option 2.

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Building & Planning - Planning

Check out our online mapping tool, EPIC, to learn more about the Comprehensive Plan and zoning classification to of your property, as well as potential environmental constraints.
Arrange a free staff consultation to get preliminary feedback from County staff that will help you with your project.
Apply for Planning Clearance, which is the first step in official review of your project (insert link https://www.co.cowlitz.wa.us/594/Planning-Clearance
If you don’t own the property yet, but want to start the planning process, you will need a signed letter of authorization from the owner.

There are land use setbacks established by zoning. There may also be setbacks required by the Building Code, Fire Code, and/or to meet environmental regulations. Talk with a Planner and staff from the Building Division to learn more.

3. Can I meet with County staff to discuss my project?: Sure! Please see our staff consultation page for information on arranging a free preliminary meeting with County staff.

If you are planning a project, you can apply for Planning Clearance, which is valid for 5 years. You will be assigned an address as part of that process.
If you need an address but have no plans to develop the property in the near future, you can apply for that separately. Please contact a Planner to discuss the information needed.

Probably! Accessory dwelling units can be either attached to a primary residence or detached as a separate structure. Classic examples are a dwelling above a garage, or a cottage for rental income. ADU’s require planning approval and a residential building permit. They can be manufactured or modular homes.
The maximum size of an ADU is 1,200 square feet.
In areas classified as Urban and Suburban in the Comprehensive Plan, you may choose to build up to two ADU’s – one attached and one detached. In all other areas of the county, one ADU is allowed.
There is no restriction on owner-occupancy of the primary residence or the ADU – one or both can be occupied by tenants.
If you are using a domestic well and/or onsite septic system for the ADU, you will need to talk with the Environmental Health Unit about their requirements. Their email is omseptic@cowlitzwa.gov and phone number is 360-414-5599 - press 5 and option 2.

No, Cowlitz County does not fully plan under the State Growth Management Act, and therefore does not charge impact fees.

Public Works reviews permits for compliance with stormwater requirements. Please see their information here: include hyperlink to: https://www.co.cowlitz.wa.us/931/Stormwater-Division